Manufacturing operations often require the formation of electrical resistance welds. Electrical resistance welding (ERW), for example spot welding or seam welding, includes clamping the components of a work piece to be welded between a pair of opposed electrodes, and passing sufficient electrical current through the electrodes and components to melt and fuse the components together. Resistance spot welding (RSW) may be performed using a welding gun having copper alloy welding electrodes. One electrode may be fixed and the other electrode may be moveable with respect to the weld gun. The components to be welded may be, for example, two sheet metal panels.
Dressing of electrodes is a process to reshape or resurface electrodes when the electrodes become worn. Wear can be caused, for example, by reaction between the copper electrode and the metal sheet, which may comprise aluminum, steel, or zinc-coated steel. In the case of an aluminum sheet, aluminum may be transferred to the electrode as an oxide, metal particles, or alloyed with the copper. This transfer eventually leads to pits on the electrode surface that can be harmful to the welding process. In the case of zinc-coated steel, the copper electrode can react with zinc forming a soft brass alloy on the electrode weld face that accelerates electrode deformation. Wear can also be caused by simple deformation of the electrode from exposure to high temperatures and pressures, especially during the spot welding of steel.
Dressing of electrodes can accomplish different results depending on the design of both the electrode and the dressing blade, as well as the primary purpose for dressing. For example, heavy cutting of metal from the electrode sides, sometimes called the electrode form or shoulder, may be used primarily on deformed electrodes to maintain electrode geometry during spot welding of steel. Very little cutting would take place on the electrode weld face. Light cutting of the electrode weld face may be used to remove welding contamination and pits that have formed during the spot welding of aluminum alloys. In general, the dressing process for electrodes used in spot welding uses hardened blades that rotate at moderate speed to machine off portions of the electrode, i.e., the electrode sides, form, or shoulder, and the weld face.